1. Field of the Invention
This invention relates to "breaking" of high viscosity fluids containing xanthan gums which are used in industrial and oil field operations. Breaking refers to an intentional reduction in the viscosity of a high viscosity fluid.
In a number of industrial and oil field operations, there is a need for a fluid with an initial high viscosity to suspend particulate matter and a final low viscosity to permit the suspended matter to settle out. The fluid's viscosity must be able to be intentionally and controllably reduced such that the suspended matter will settle out when desired.
2. Description of the Related Art
In oil field operations, there are several uses for high viscosity fluids which may subsequently be converted into low viscosity fluids. A high viscosity fluid has a greater propensity to keep insoluble, particulate matter suspended therein. If this fluid's viscosity is substantially lowered, the suspended particles will settle out.
In the oil field, there are several operations in which a fluid's ability to initially hold and later drop this suspended particulate matter is beneficial. These operations include the placement of gravel packs in well completion operations, the placement of proppants in a formation after the fracturing of the formation, and other applications, such as drilling fluids. For most of these operations, and especially in gravel pack and fracturing operations, it is also important to minimize gel residue once the gel is broken.
In industry, there exist several uses for a fluid which has a viscosity that can be controllably altered. These uses include transporting particulate matter, such as coal particles or mineral ore particles, through pipelines by suspending the particles in a slurry.
Polysaccharides have been particularly useful in functioning as a thickener for aqueous fluids. There are several related processes for breaking thickened aqueous fluids containing polysaccharides. In U.S. Pat. No. 4,647,385, a combination of an alkali metal or alkaline earth metal salt of hypochlorous acid and a water-soluble tertiary amine is used as a breaker for aqueous fluids containing polysaccharides as well as other thickeners including water-soluble derivatives of cellulose and synthetic water-soluble polymers. U.S. Pat. Nos. 4,250,044 and 4,560,486 discuss a breaker for aqueous fluids containing polysaccharides which combines a water-soluble tertiary amine and at least one compound selected from the group consisting of ammonium persulfates and alkali metal persulfates. While these breakers are effective on most polysaccharide thickeners, such as guar gum, hydroxypropyl guar and locust bean gum, they are not particularly effective on xanthan gum thickeners. When these breakers are applied to aqueous solutions containing xanthan gum thickeners, they are not as effective in that they do not effect a clean break. Also, when these breakers are used on xanthan gums, the degree of breaking performance cannot be controlled. Accordingly, there exists a need for improving breaker systems used on xanthan gum thickeners.